This invention relates to a device for automatically controlling the temperature of intake air for an internal combustion engine, and more particularly to a thermostatic valve of a construction, as disclosed in our copending U.S. patent application Ser. No. 739,190, which serves dual functions; sensing a change in temperature of the engine room or the like and controlling the quantity of intake air supply to the engine proportionally according to the temperature change, and also controlling a negative pressure motor so as to proportion cold and hot air in a mixture being supplied to the carburetor of the engine or switch from cold air supply to hot air supply or vice versa, in response to the temperature change and to the negative pressure in the intake manifold space downstream of the throttle valve of the engine.
For use with internal combustion engines of automobiles and the like, a thermostatic valve has already been proposed which combines, in a unitary construction, a thermostatic valve for sensing the temperature of the intake air being supplied to the carburetor when the air temperature is low, especially in winter, and allowing the negative pressure in the intake manifold space downstream of the throttle valve to act upon a negative pressure motor according to the intake air temperature sensed, thereby controlling the motor so as to adjust the cold and hot air supply to the carburetor, with another thermostatic valve which, when the atmospheric temperature is high, for example in summer, particularly during idling, enables additional air to be supplied to the intake manifold lest the gaseous mixture in the manifold become overrich.
The conventional thermostatic valve just described uses one or more bimetals as the temperature sensor and actuator. For the control over the broad temperature range, from low to high temperatures, each bimetal must be of very large dimensions. Accordingly the increased weight and size raise the cost of the element. Moreover, under vibratory conditions, the bimetal exhibits a serious disadvantage of errorneous functioning due to vibration.
A further important disadvantage of the thermostatic valve has been that, because the control of cold and hot air supply to the carburetor is effected by allowing the negative pressure in the intake manifold space downstream of the throttle valve to act upon the negative pressure motor, the negative pressure in the intake manifold can drop during full-load running in a cold season, for example, below the level for the motor to permit the hot air supply, resulting in cold air intake and even icing of the carburetor.
A thermostatic valve of a type using a thermally expandable element whose volume changes with the temperature has also been proposed. It comprises a cylindrical valve body and a piston-like valve element disposed therein to be actuated by the expansion of the thermally expandable element, so that the air flow into the negative pressure motor and the intake manifold is controlled by the sliding motion of the valve element in the valve body. In order that the valve element may slide smoothly within the valve body, a small clearance must be provided between the outer surface of the element and the inner surface of the valve body. This clearance can in some cases admit excess air to the negative pressure motor and the intake manifold. After an extended period of the clearance sometimes grows so large that the manifold may no longer exert a negative pressure upon the motor. This leads to a major disadvantage of unreliability in performance.